The xport1 mutant displays a combination of protein accumulation in the secretory pathway (like ninaE318) and a severe reduction in TRP protein (like trp343). Like the xport1 mutant, the ninaE318

mutant displayed considerable ER membrane accumulations and dilated Golgi at 1 day old ( Figure 7B). In contrast, the trp343 null mutant showed no sign of secretory pathway membrane accumulations ( Figure 7C). The secretory pathway defects were light independent, FG-4592 purchase as the membrane accumulations were still present in 1-day-old xport1 and ninaE318 mutants that had been reared in constant darkness ( Figures 7D and 7E). At 2 weeks, trp343 displayed a severe retinal degeneration ( Figure 7H) that was comparable to that observed in the xport1 mutant ( Figures 6C and 6D). In contrast, the ninaE318 mutant exhibited milder pathology

at 2 weeks ( Figure 7G). As was shown for xport1 ( Figure 6E), the retinal degeneration was significantly attenuated in this website trp343 mutants reared in constant darkness for 2 weeks ( Figure 7J). Taken together, these results indicate that the retinal degeneration in the xport1 mutant is due to the combined detrimental effects of protein aggregation in the secretory pathway and misregulation of Ca2+ levels in the absence of TRP. More specifically, the light-independent membrane accumulations in xport1 are likely the result of defects in TRP and Rh1 trafficking, MYO10 while the light-enhanced retinal degeneration is likely due to the near complete loss of TRP channels in the rhabdomere. Given that two other chaperones, namely NinaA and calnexin, are also essential for Rh1 maturation and trafficking

(Colley et al., 1991 and Rosenbaum et al., 2006), XPORT may play a critical role in a conserved protein-processing pathway with these chaperones. To investigate the temporal sequence of calnexin, NinaA, and XPORT chaperone activity for Rh1, we conducted genetic epistatic analyses by generating double-mutant flies. In all three single mutants, Rh1 was severely reduced (Figure 8A). However, in the ninaAP269 mutant, a substantial amount of Rh1 was detected in the immature high MW form. The ninaAP269;calnexin1 double mutant displayed severely reduced levels of Rh1 in the mature low molecular weight form, a phenotype characteristic of the calnexin1 mutation alone ( Figure 8A). These results demonstrate that calnexin functions upstream of NinaA in Rh1 biosynthesis. Consistent with this finding, calnexin was entirely digested by both endoglycosidase H (Endo H) and peptide N-glycosidase F (PNGase F) ( Figure S2D). Endo H selectively cleaves high mannosyl residues on glycoproteins that have not yet been processed in the Golgi and thus Endo H sensitivity implicates glycoproteins as ER residents. Therefore, calnexin is restricted to the ER. NinaA, however, was only partially digested by Endo H and fully digested by PNGase F ( Figure S2D).